Beginning in the 1950s, a family of 40 mm grenade launchers was developed to assist soldiers to cover the area between the longest range of the hand grenade (30-40 yards) and the middle range of the 60 mm mortar (300-400 yards). The family of 40 mm grenade launchers includes: the M79, the M203 and the M203a. Each of the 40 mm grenade launchers fires various types of 40 mm cartridges including: high explosive (“HE”) rounds, projectile practice rounds, chemical rounds, buckshot rounds and pyrotechnic signal and spotting rounds.
The 40 mm M79 grenade launcher resembles a large bore, single aluminum barrel, sawn off shotgun. The M79 grenade launcher was developed in the 1950s and was first delivered to the US Army in 1961.
The 40 mm M203 grenade launcher was developed to attach to an existing M-16 rifle and M-4 carbine. It consists of a 10-inch long aluminum barrel and a receiver clamped underneath an M-16 barrel. A variation of the M203 is the M203a, which consists of an 8-inch long aluminum barrel and a receiver clamped underneath a M-4 carbine. The working pressure of each of the M79/M203/M203a is 3000 psi.
Because the HE rounds require an arming delay of an internal fuze device, and because of the blast radius associated with the high explosive, the HE round is not effective at close ranges.
To provide close range potential for an M79, M203 or M203a grenade launcher, a shotgun shell type round was developed, known as an XM576. The XM576 includes 20 No. 4 buckshot pellets (each 0.24-inch in diameter) that leave the M79/M203/M203a muzzle at only 885 feet per second. Unfortunately, the XM576 has not performed as hoped either by the military or by law enforcement.
In another effort to improve the close range effectiveness of the M79/M203/M203a family of grenade launchers, a 12-gauge sub-caliber device was developed and was issued to service personnel in Vietnam on an experimental basis. The sub-caliber device consisted of a steel rim and liner with a spring-loaded extractor inside a 40 mm plastic bushing. The device was about 9-inches long and would accept any commercial 12-gauge buckshot load. Other such devices have been constructed in lengths of 5-inches overall. Unfortunately, neither the XM576 nor the sub-caliber devices can provide satisfactory shot patterns or velocity at ranges beyond approximately 10 yards.
What is needed is a device that can be used in existing M79/M203/M203a grenade launchers, or other sizes of low pressure launching systems, to provide a close quarter battle load and at the same time, overcome the problems that exist with the XM576 round and sub-caliber adapters.